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Index to Creationist Claims,  edited by Mark Isaak,    Copyright © 2005
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Claim CH321:

Parasites are degenerate forms of free-living or mutualistic organisms. They became parasites when something went wrong as a result of the Fall. For example, the parasite came to invade the wrong host or the wrong organ within the host, or it changed to harm the host where it did not before.


Mace, Stephanie R., B. A. Sims, and T. C. Wood, 2003. Fellowship, creation, and schistosomes. Impact 357 (Mar.).


  1. Parasites are far from degenerate. They have lost features that are familiar to us as nonparasites, but they also have acquired many other highly sophisticated features and abilities, allowing them to find their hosts, to survive their hosts' immune systems (often multiple hosts for one parasite), and to survive some otherwise hostile environments within their hosts. Creationists themselves tout the complexity of the immune system; does not circumventing an immune system deserve at least as much credit? Fast-evolving viruses like the common cold show that such adaptations are evolving all the time.

    Here are just a few features that parasites have. Similar adaptations are common (Hajek and St. Leger 1994; Zimmer 2000):

  2. Evolution often goes the other way; parasites that initially are very harmful become more benign to their host over time. The virulence of a pathogen is generally predictable on the basis of evolutionary principles. For example, parasites are less virulent at low host population densities where the parasites risk destroying available hosts and themselves with them (Nesse and Williams 1994, 57-61; Zimmer 2000, 151-155).

  3. Why do organisms have defenses against pathogens in the first place? They would not have been needed in a pre-Fall world without pathogens, and their complexity and effectiveness show that features such as immune systems are not degenerate forms themselves.


  1. Eberhard, William G., 2000. Spider manipulation by a wasp larva. Nature 406: 255-256.
  2. Hajek, A. E. and R. J. St. Leger, 1994. Interactions between fungal pathogens and insect hosts. Annual Review of Entomology 39: 293-322.
  3. Moller, Anders Pape, 1993. A fungus infecting domestic flies manipulates sexual behaviour of its host. Behavioral Ecology and Sociobiology 33: 403-407.
  4. Nesse, R. M. and C. G. Williams, 1994. (see below)
  5. Zimmer, Carl, 2000. Parasite Rex. (see below)

Further Reading:

Nesse, Randolph M. and George C. Williams, 1994. Why We Get Sick, New York: Times Books.

Sapolsky, Robert, 2003. Bugs in the brain. Scientific American 288(3) (Mar.): 94-97.

Zimmer, Carl, 2000. Parasite Rex: inside the bizarre world of nature's most dangerous creatures. New York: The Free Press.
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created 2003-7-23, modified 2005-1-14